grab sample

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grab sample

In public health and medical statistics, a chaotic set of data from which conclusions are injudiciously drawn. Because the sample is not carefully randomized or scientifically selected, the conclusions derived from such sample groups may be inaccurate.
See also: sample


1. a specimen of fluid, blood or tissue collected for analysis on the assumption that it represents the composition of the whole.
2. for statistical purposes a small collection of individual units taken from the population which is under investigation on the assumption that they represent the characteristics of the entire population.

EPSEM sample
acronym for 'equal opportunity of selection method'.
grab sample
sample of greasy wool taken at random by a special machine from each bale on the sale floor. Buyers price the bale on the basis of the appearance of the grab sample and the objective measurements.
multi-stage random sample
with very large populations it may be desirable to arrange the data into groups on one criterion, e.g. address by area of postcode, and to select randomly from within this group, then select from within this sample to obtain randomly a representative number of specimens, such as dogs of each age group.
random sample
the selection from a population of the units which are to constitute the sample of that population is made in such a way that each unit of the population has an equal chance of being selected. Called also simple random sample.
simple random sample
see random sample (above).
stratified random sample
the data is arranged into subsets or strata based on the possession of certain characteristics which are common to the members of the subset. The selection of units to comprise the sample of the parent population is arranged so that the proportional representation of each subset in the final sample fits a prearranged schedule.
volunteer sample
sample donated by interested parties; a biased sample because it does not represent all sections of the population. Called also self-selection.
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References in periodicals archive ?
EPA makes clear two points: grab samples are inadequate and under-report treatment efficiency, and the use of low-paid, unsupervised personnel to collect samples is inappropriate.
EPA publication compared grab samples and composite samples to reach their conclusions.
Composite of grab samples over 25 ft of strike of main vein - 0.
8 % copper in grab samples, and gold values taken from grab samples of boulders along the mineralized trend range from 1.
Grab samples across this newly discovered vein have turned up results ranging from 0.
The Yellow Brick Road zone is a steeply dipping gold-bearing zone with grab samples containing 5.